1. Field of the Invention
The invention relates to an agitator mill comprising a grinding receptacle which defines a substantially closed grinding chamber by means of a receptacle wall and, comprising an agitator which is rotatably drivably disposed in the grinding receptacle in a direction of rotation and which is cup-shaped with respect to a common central longitudinal axis, and which has an annular cylindrical rotor which is provided with implements extending as far as into the vicinity of the receptacle wall, and comprising an interior stator which is disposed within the rotor, which is joined to the grinding receptacle, and which has a closed outer wall, wherein the annular cylindrical grinding chamber is formed between the receptacle wall and the rotor and receives auxiliary grinding bodies with a diameter c, and wherein an annular cylindrical interior chamber in the shape of an annular gap is formed between the rotor and the outer wall of the interior stator, said interior chamber being disposed coaxially within the grinding chamber and connected thereto via a deflection conduit, and wherein the grinding chamber is at least partially filled with auxiliary grinding bodies, and wherein a grinding-stock supply chamber, which is disposed upstream of the grinding chamber and opens into the latter in a direction of flow, and a protective screen, which is disposed downstream of the interior chamber in the direction of flow, are disposed approximately on the same side of the grinding receptacle for the grinding stock to pass through, and wherein auxiliary-grinding-body return conduits are provided in the agitator for returning the auxiliary grinding bodies from the vicinity of the protective screen into the grinding chamber, said return conduits connecting the end of the interior chamber to the beginning of the grinding chamber.
2. Background Art
Such an agitator mill is known from U.S. Pat. No. 5,062,577. In this agitator mill, the auxiliary grinding bodies are centrifuged from the flow of grinding stock and auxiliary grinding bodies via the auxiliary-grinding-body return conduits before said flow reaches the protective screen. The basic function of the protective screen is to collect worn-out auxiliary grinding bodies which are too light to be thrown out via the auxiliary-grinding-body return conduits, thus serving as a throttle device for generating a counter-pressure counteracting the flow of grinding stock. The agitator is provided with agitator implements protruding into the exterior grinding chamber. When using extremely small auxiliary grinding bodies, it is not ensured that the auxiliary grinding bodies will not eventually reach the protective screen, thus gradually clogging the latter. In particular when using extremely small auxiliary grinding bodies, it is required to use correspondingly fine protective screens which in turn may be damaged very easily, should they be hit by auxiliary grinding bodies. If, however, relatively viscous grinding stocks are to be treated by using auxiliary grinding bodies of a usual size, a partially clogged protective screen leads to a substantial pressure build-up in the agitator mill, which also results in a disturbance of the grinding process.
An agitator mill is known from EP 0 504 836 B1 which has a cup-shape rotor disposed in a cylindrical housing, said rotor being provided with passage slots along the length thereof. An interior stator comprising a protective screen is disposed within the rotor. The exterior grinding chamber is provided with implements that are fixed to both the rotor and the wall delimiting the grinding chamber. This agitator mill is not suitable for the use of extremely small auxiliary grinding bodies. Moreover, said mill is subject to the same problems as already described above.
An agitator mill is known from U.S. Pat. No. 5,011,089, said agitator mill having a rotor with paddle-shaped implements disposed on the outside thereof. A protective screen is disposed within the rotor. The rotor is composed of axially parallel bars to which the paddle-shaped implements are fastened. The grinding stock is supplied radially. Owing to the paddle-shaped design of the agitator implements, this agitator mill ensures a concentration of auxiliary grinding bodies to be obtained in the area of the receptacle wall; a defined grinding, in particular by means of extremely small auxiliary grinding bodies as well as a reliable separation of the auxiliary grinding bodies without the risk of operational failures is however not obtainable either. Since the grinding stock flows through the packing of auxiliary grinding bodies in a radial direction, the grinding stock is subject to a grinding process over a very short distance only. Accordingly, if the grinding stock passes through the agitator mill only once, only a moderate grinding progress is obtained.
An agitator mill of the generic type is known from U.S. Pat. No. 5,894,998, said agitator mill having a protective screen fixed to the cup-shaped rotor which is sealed against the interior stator by means of a mechanical seal. The protective screen thus co-rotates with the rotor, thereby ensuring that auxiliary grinding bodies reaching said filter are thrown out even more efficiently.
An agitator mill is known from U.S. Pat. No. 5,346,124, with implements having transport surfaces being fixed to the rotor thereof and imparting a momentum to the grinding stock and the auxiliary grinding bodies in the direction from the grinding-stock inlet to the grinding-stock discharge.